Merge pull request #7720 from misha-ridge/atomic-charts-cache

Make the charts cache safe in presence of several Helm instances

pkg/downloader/chart_downloader.go

@@ -72,6 +72,31 @@ type ChartDownloader struct {
 	RepositoryCache  string
 }
 
+// atomicWriteFile atomically (as atomic as os.Rename allows) writes a file to a
+// disk.
+func atomicWriteFile(filename string, body io.Reader, mode os.FileMode) error {
+	tempFile, err := ioutil.TempFile(filepath.Split(filename))
+	if err != nil {
+		return err
+	}
+	tempName := tempFile.Name()
+
+	if _, err := io.Copy(tempFile, body); err != nil {
+		tempFile.Close() // return value is ignored as we are already on error path
+		return err
+	}
+
+	if err := tempFile.Close(); err != nil {
+		return err
+	}
+
+	if err := os.Chmod(tempName, mode); err != nil {
+		return err
+	}
+
+	return os.Rename(tempName, filename)
+}
+
 // DownloadTo retrieves a chart. Depending on the settings, it may also download a provenance file.
 //
 // If Verify is set to VerifyNever, the verification will be nil.
@@ -101,7 +126,7 @@ func (c *ChartDownloader) DownloadTo(ref, version, dest string) (string, *proven
 
 	name := filepath.Base(u.Path)
 	destfile := filepath.Join(dest, name)
-	if err := ioutil.WriteFile(destfile, data.Bytes(), 0644); err != nil {
+	if err := atomicWriteFile(destfile, data, 0644); err != nil {
 		return destfile, nil, err
 	}
 
@@ -117,7 +142,7 @@ func (c *ChartDownloader) DownloadTo(ref, version, dest string) (string, *proven
 			return destfile, ver, nil
 		}
 		provfile := destfile + ".prov"
-		if err := ioutil.WriteFile(provfile, body.Bytes(), 0644); err != nil {
+		if err := atomicWriteFile(provfile, body, 0644); err != nil {
 			return destfile, nil, err
 		}